Water supply and zone demand worksheet

Use this worksheet to organize two different measurements: open-outlet flow and available flow at the pressure your nozzles require. It does not measure your property or certify a zone design. Inputs stay in this browser page and are not sent to our planner.

1. Record an open-outlet observation

If you can safely collect water from an existing outdoor outlet without changing plumbing, record the container volume in US gallons and the time to fill it. Repeat three times under the same conditions. Do not open a meter enclosure, alter a pressure regulator or disconnect backflow protection for this test. A bucket result describes that outlet with little downstream resistance; it does not prove that the same flow remains available at sprinkler operating pressure.

Bucket observation

Container volume (US gallons)Fill time 1 (seconds)Fill time 2 (seconds)Fill time 3 (seconds)

Calculate bucket observation

No observation calculated.

2. Compare a separately verified design allowance

Ask a qualified irrigation professional to establish available flow at the required operating pressure at your proposed connection, accounting for the supply, elevation and equipment losses. Static pressure is measured with no water moving; it is not the pressure a running zone will receive. Enter that independently verified flow allowance below. The bucket calculation never fills this field automatically.

Demand comparison — all flows in US gallons per minute

Verified available design flow at required pressureManufacturer flow per nozzle at that operating pressureNumber of identical nozzles

Compare flow demand

This comparison does not check pipe losses or coverage.

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Worked example: what the result can establish

A fictional 5-gallon bucket filling in 30, 32 and 31 seconds gives a median open-outlet reading of 9.68 GPM. That does not establish a 9.68 GPM design capacity. Separately, suppose a professional verifies a 6 GPM allowance at the required operating pressure. Four identical nozzles rated at 1.2 GPM each demand 4.8 GPM, leaving 1.2 GPM within that entered allowance. This arithmetic says nothing about whether the last head receives enough pressure or whether the lawn has uniform coverage.

Before the draft becomes a purchasing list

1. Verify dimensions, elevations, planting areas and the proposed connection in the field.
2. Record the measured static pressure and the verified flow/pressure operating point separately, including who measured them and under what conditions.
3. Check each nozzle model against its manufacturer’s performance chart at the pressure expected at that head. Different models cannot be represented by one shared flow input.
4. Have pipe length, diameter, fittings, valve, filter and backflow losses reviewed. A percentage reduction of bucket flow cannot replace this work.
5. Ask the water supplier which backflow protection and approvals apply before making a connection. Locate buried services through the appropriate local process before digging.
6. After installation, check actual zone operation and distribution. A drawing does not prove coverage or an appropriate watering schedule.

Technical references

The Rain Bird irrigation design manual explains pressure, flow and losses. The Hunter technical handbook provides equipment and hydraulic reference information. EPA WaterSense describes professional irrigation assessment. These references inform the explanation; they do not endorse this tool.

Understand pressure and flow · Editorial standards · All guides